Conventional portable computers include a display housing rotatably connected to a base with a hinge assembly. The display housing is rotatable about the hinge assembly between an open position, in which the display, or "LCD," and a keyboard integrated into the base are exposed for use, and a closed position, in which the display housing functions as a cover for the base. Preferably, the hinge assembly is such that the display housing will be retained by the hinge assembly at nearly any angle selected by a user relative to the base.
In the past, this has been accomplished by relying on friction to hold the display housing at the selected angle. This technique suffers from several deficiencies. In particular, the friction necessary to support the weight of the display housing is often so great that both hands are required to open the computer and to pivot the display housing about the hinge. Moreover, hinge assemblies that rely on friction have a tendency to cause the display housing to slam against the base when the angular position of the display housing relative to the base reaches a certain minimum.
As an alternative, hinge assemblies have been provided with clutch mechanisms. One such clutch mechanism includes a friction component and a torsion spring component. The spring counteracts the weight of the display housing when the display housing is open, such that the friction component need only be strong enough to support the open display housing during times when the computer is subjected to vibration or the like. This solution reduces the amount of force necessary to adjust the angular position of the display housing and allows the use of a smaller, lighter friction component.
With the increasing modularity of computer systems, it is valuable to have components that can migrate across systems. Clutches have historically not been capable of use in more than one computer system because they are designed to resist a specific torque, and are therefore designed for a specific LCD configuration. For example, a clutch designed for use in a portable computer having a 13 inch LCD will likely be designed with less torque than one for use in a portable computer having a 15 inch LCD. Using a clutch with too much torque will result in many of the same difficulties associated with hinge assemblies that rely on friction, as described above. Alternatively, using a clutch with too little torque will result in the display housing's not being retained in the position selected by the user and either slamming shut, when the relative angle between the display housing and the base is less than 90 degrees, or falling back when the relative angle between the display housing and the base is greater than 90 degrees.
The fact that clutches are presently designed for use with a particular portable computer system is problematic for computer manufacturers that produce several different portable computer configurations. In particular, assembly of a computer using a hinge assembly with the wrong clutch (i.e., the wrong torque) will result in improper mechanical operation of the computer, depending on whether the torque is too great or too small, as described above. In addition, it is expensive to have to maintain an inventory of hinge assemblies for each of a variety of computers.
Therefore, what is needed is an adjustable torque clutch mechanism for incorporation into the hinge assembly of a portable computer.